This invention relates generally to valves and more particularly to check valves for severe service applications where high impact loads would be expected.
As is known, normally, when a check valve is subject to rapid (dynamic) changes in flow (direction or magnitude) its moving parts acquire kinetic energy. If the flow increases in magnitude the direction of motion of the poppet will be called opening. If the flow decreases in magnitude or reverses, the poppet's direction of motion will be called closing. During periods of steady flow the poppet will (eventually) acquire an equilibrium position where, in the absence of other effects, the fluid resistance forces against its face are balanced by the forces exerted by the valve body and/or the spring. Check valves used in reciprocating pumps and compressors (both for the inlet and discharge of each cylinder) are subjected to dynamic flow within each cycle. Therefore, the poppet element is in motion during at least part of each cycle. The accelerations and velocities of the poppet are not negligible. Unless the dimensions of the valve are sufficient to provide no limit to the poppet motion, the poppet will, when opening strike a stop of the valve. When closing, the poppet will eventually strike the valve seat. The problem is that when the poppet strikes either the stop or the valve seat it may rebound, and will generally produce forces and stresses on the seat, stop and faces of the poppet. Rebounds from the seat result in a lag between the time at which the valve should close and the time at which the poppet comes to rest in the closed position. This delay results in reverse flow in the reciprocating compression equipment. Should the impact stresses induced in the seat stop, or the poppet be of sufficient magnitude, yielding, deformation and finally fracture of the valve component can result.
In U.S. Pat. No. 4,447,195 (Schuck) and U.S. Pat. No. 4,559,786 (Schuck), both of which are assigned to the same assignee as this invention, there is disclosed a pump for compressing a low temperature high density liquid gas, e.g. liquid helium. The pump includes a discharge valve having a movable poppet and making use of plural elastic cushion elements. These elements are provided to cushion the impact forces extant during the cyclical opening and closing of the valve.
In U.S. Pat. No. 4,967,790 (Ganske) there is disclosed a gravity closed swing check valve which is designed to exhibit resistance to impact damage. To that end the valve includes a clapper which is arranged to engage a downstream surface that is semi-spherical and convex. The body of the valve forms a concave semi-spherical cavity. The radii of the clapper and cavity surfaces is the same. The clapper is positioned so that its downstream surface bears evenly across the surface of the body cavity, when the clapper is in the fully open position. Thus the cavity surface of the body acts as a stop for the clapper and the area of stop surface is relatively large.
While the aforementioned prior art valves may be suitable for their intended purposes they nevertheless leave something to be desired from one or more of the standpoints of resistance to impact force induced damage, reliability, complexity, cost. In addition, due to scaling factors, the impact stresses increase as overall valve size increases. Because of this, larger pump valves face increased stresses and are prone to damage as compared to smaller valves.